Fundamentals in fighting games are generally considered whiff punishing / punishing unsafe moves / throwbreak and spacing / movement , however there are fundamentals that belong in separate genres like 2d fighting games have anti airs while in the 3d genre there is sidestepping and knowledge of duckable strings.
That said Tekken requires a good amount of practice for advanced movement , knowing when and where to sidewalk and when to sidestep and awareness on which side you're in the screen ( many confuse left and right in the heat of a fight especially when switching sides ) , it's extremely different than playing MK , fundamentals are there but the engine is very different and needs adaptation.
When i do talk about Mishimas hard to master it's because they are monsters at spacing and punishing while still having good pressure up close but that said you have to master EWGF wich is easier said than done , you'll understand when you'll try punishing -14 moves ( EWGF is 14 frames if executed perfectly , kazuyas should be 13 iirc ) , many characters have it way easier ( like bryan has a 14 frame launcher Jet uppercut and the motion its a simple f n b2 )